Biochemical Tests

• Water

  1. Fundamental to all blood tests

  2. Concentration = mass/volume

  3. Patient’s hydration status is important

  4. N.B. water volume is regulated by the kidney, if there are issues with renal function this can result in either water retention or excess fluid loss
• Sodium

  1. Major extracellular cation

  2. Function: Maintain osmolality

  3. Water intake and loss is required to maintain a constant sodium concentration

  4. Major route of sodium excretion is via the kidneys

  5. Antidiuretic hormone

  6. Aldosterone

  7. Thirst

  8. Changes in serum sodium concentration are usually due to: Diet (rich or low in sodium), The amount of water in the blood, Kidney function
• Hypernatraemia

  1. Defined as a plasma sodium concentration of: > 145 mmol/L

  2. Causes: Water depletion, Loss of water in excess of sodium, Decreased fluid intake, Increased sodium in
• Management of Hyponatraemia


  Identify and correct the underlying cause, Depending on cause: Increased salt intake, Fluid restriction, If needed: Mild – moderate: Slow – sodium, 4 – 8 tablets (2.4 – 4.8g), Demeclocycline 900 – 1200mg daily in divided doses, Severe: I/V NaCl
• Management of Hypernatraemia

  Identify and treat underlying cause, Replace body water orally or intravenously with Dextrose 5% w/v
• Hypernatraemia

  1. Defined as a plasma sodium concentration of > 145 mmol/L

  2. Causes: Water depletion, Loss of water in excess of sodium, Decreased fluid intake, Increased sodium intake or retention in excess of water, Mineralocorticoid excess, Medication, Renal failure
• Drugs associated with increased sodium


  • Corticosteroids
  • NSAIDs
  • Laxatives
  • Lithium
• Potassium

  Intracellular Cation – 98%, Essential for normal cell function, Regulated by aldosterone, cortisol, insulin and glucose, Changes in potassium levels have a profound effect on
• Potential Causes of Hyponatraemia

  • Medication
  • Mineralocorticoid deficiency
  • Water/fluid excess (SIADH, Certain disease states)
  • Abnormal losses of sodium (Diarrhoea, DKA)
  • Alcohol excess
  • Severe burns
  • Malnutrition
  • Dilution of blood sample by IV fluids
• Remember, do not increase levels too quickly due to the risk of osmotic demyelination
• Hyponatraemia

  Low sodium is defined as a serum sodium concentration below 135mmol/L
• Signs and Symptoms of Hypernatraemia


  • Dry skin
  • Postural hypotension
  • Oliguria
  • Thirst
  • Confusion
  • Drowsiness, lethargy
  • Extreme cases – coma (>155 mmol/L)
• Potassium

  • Regulated by aldosterone, cortisol, insulin, and glucose
  • Changes in potassium levels have a profound effect on the nervous and cardiovascular system
  • Fatal in extreme cases
• Community Management of Hyperkalaemia


  • All trusts will have their own local guidelines
  • Refer to hospital if >6.5mmol/L, acute ECG changes and >5.5 mmol/L, rapid rise
  • Mild (5.5 – 5.9): Correct underlying cause, repeat blood test, medication review, and dietary changes
  • Moderate (6 - 6.4): Carry out an ECG, assess course of action based on this, review patient
• Main route of potassium loss is via the kidneys with small losses in faeces and the skin
• Causes of Hyperkalaemia

  • Medication
  • Renal issues
  • AKI
  • CKD
  • Rhabdomyolysis
  • Hypoaldosteronism
  • Advanced CCF
  • Acidosis
  • DKA
  • Severe tissue damage
  • Hormonal effects
  • Fragile blood cells
  • Consider diet
• Management of Hyperkalaemia


  1. Assess patient: ABCDE

  2. Identify cause/stop potentially offending drugs immediately

  3. Rule out pseudohyperkalaemia

  4. Ensure adequate hydration

  5. Consider severity

  6. Severe/ECG changes: MEDICAL EMERGENCY
• Potassium is an intracellular cation, essential for normal cell function
• Factors influencing potassium levels

  • Acid-base disturbances
  • Catabolic states
  • Anabolic states
  • Insulin secretion
• Severity levels of Hyperkalaemia


  • Mild: 5.5 – 5.9 mmol/L
  • Moderate: 6.0 – 6.4 mmol/L
  • Severe: ≥ 6.5 mmol/L
• Hyperkalaemia is often identified in the community setting
• Potassium is mainly absorbed in the small intestine and eliminated via the kidneys
• Do not increase levels too quickly due to the risk of osmotic demyelination
• Signs and Symptoms of Hyperkalaemia include fatigue, muscle weakness, abnormal cardiac conduction, chest pain, palpitations, ECG changes, and in severe cases, cardiac arrest
• Hospital Management of Hyperkalaemia

  1. Step 1: Protect the heart

  2. Step 2: Shift potassium into cells

  3. Step 3: Remove potassium from the body
• Step 4: Monitoring

  1. Continuous cardiac monitoring where ECG features are present

  2. Potassium levels every 2 – 4 hours

  3. Blood glucose levels

  4. Baseline, 15, 30, 60, 90, 120 minutes and up to 6 hours post dose
• Step 3: Remove potassium

  1. Potassium exchange polymers

  2. Anion exchange resin - Calcium resonium: 15g TDS

  3. Potassium binders - Patiromer calcium, Lokelma (sodium zirconium cyclosilicate), licensed for use alongside standard care for the emergency treatment of acute life-threatening hyperkalaemia

  4. Dialysis
• Step 1: Protect the heart

  1. If there are ECG changes: 30ml of 10% calcium gluconate IV OR 10ml of 10% calcium chloride IV

  2. Antagonises cardiac excitability

  3. NB: Patients on digoxin, this is an unlicensed indication for the medication
• Drugs causing Hypokalaemia

  • Salbutamol (especially in high doses)
  • Thiazide diuretics
  • Loop diuretics
  • Insulin
  • Steroids
  • Chronic laxative abuse
• Hospital Management of Hyperkalaemia

  1. Step 1: Protect the heart

  2. Step 2: Shift potassium into cells

  3. Step 3: Remove potassium from the body

  4. Step 4: Monitoring

  5. Step 5: Prevention
• Signs and Symptoms of Hypokalaemia

  • Hypotonia
  • Cardiac arrhythmias
  • Muscle weakness
  • Fatigue
  • Confusion
  • Paralytic ileus
• Step 2: Shift potassium into cells

  1. Insulin-glucose infusion: 10 units of soluble insulin in 250ml dextrose 10%

  2. 10 – 20mg salbutamol nebuliser (IHD)

  3. Shifts into the cells temporarily, this is a holding measure only, does not reduce total body potassium, will start to leak back into extracellular space (2 – 6 hours)
• Management of Hypokalaemia

  Depends on the severity, Correct underlying cause or disease process, Use potassium sparing drugs, Oral treatment, Intravenous treatment
• Causes of Hypokalaemia: Medication, Decreased intake, Abnormal losses, D&V, Ileostomy, Acid-base disturbances
• Step 5: Prevention

  Stop nephrotoxic medications and drugs known to contribute to hyperkalaemia
• Management of Hypokalaemia

  1. Depend on the severity

  2. Correct underlying cause or disease process

  3. Use potassium sparing drugs

  4. Oral treatment

  5. Intravenous treatment
• Haematological Laboratory Tests
• Increased risk of digoxin toxicity in the presence of hypokalaemia
• No specific symptoms associated with changes in chloride levels
• Creatinine is the end product of muscle metabolism